The waste heat generated by car engines, power plants, home furnaces and other fossil fuel-burning machinery plays an unappreciated role in influencing regional climates, new computer simulations suggest. By altering atmospheric circulation, human-made heat may raise temperatures by as much as 1 degree Celsius during winter in the northernmost parts of the world.

The finding may help explain why current climate simulations, which account for the heat-trapping effects of greenhouse gases but n...